The present invention relates to a composition for disseminating fine powders. Finely divided powders have found important uses in connection with fire extinguishers, pesticides, medicinal and cosmetic products, etc. This invention is broadly applicable to any of these products, but will be illustrated with reference to fire extinguishing agents.
A major problem in connection with disseminating conventional powder dissemination compositions has been the packing and clogging of the powders. In particular, conventional powder dissemination compositions are subject to the settling of finely divided powder particles which form masses. The settled powder masses are difficult to break up and tend to clog feed pipes, valves, nozzles and other parts of the apparatus used to disseminate the particles.
Another disadvantage of conventional finely divided powder dissemination compositions has been the relatively high volume occupied by the finely divided powders which have a unimodal particle size distribution. The interstitial spaces between the powder particles occupy a large proportion of the total volume of the total composition. This has resulted in relatively small weight capacities per unit volume for the powder dissemination composition.
In addition, the powder particles of conventional powder dissemination compositions have a tendency to agglomerate or sinter. This causes difficulties in terms of discharge of the powders and makes it necessary to add means for deagglomeration of the agglomerated or sintered powders. This is often difficult and sometimes impossible. As a result, it is often necessary to avoid using very fine particles, such as in the micron size range, which effectively form a cloud to smother a fire.
Another problem with prior art compositions occurs when it is desired to use more than one type of powder in the composition but it is not possible to mix them because they react with each other. This problem would occur, for example, when it is desired to use bicarbonates with acid phosphates.
The present invention is clearly distinguishable from conventional powder dissemination compositions and is an improvement over the composition disclosed in U.S. Pat. No. 3,402,665 of Tarpley, Jr. et al., which is believed to be the closest prior art. The patent discloses a non-pyrotechnic disseminator wherein the material to be disseminated may comprise finely divided powders suspended within a gelled liquid which comprises at least a portion of liquefied gas. There is no mention in the patent that the powders have any particular particle size distribution. Accordingly, the composition of the present invention has a distinct advantage over the patented composition due to the higher weight to volume ratio made possible by utilizing powders having at least a bimodal particle size distribution.